1. Field of the Invention
The present Invention in the area of telecommunications, is directed to the distribution of digital television signal and also solution based on parallel transmission of contributing regional TV channels to the broadcast center and to the transmitters and also solution for transmitting prerecorded content, like advertisement and also deploying adaptive coding and modulation when using DVB-S2 at distribution path and solution for eliminating additional time delay, caused e.g. by time slicing in DVB-H networks.
2. Background Art
Currently digital TV networks for provisioning of fixed or mobile TV and radio services are being projected and built. These networks are comprised of varying number of transmitters (sometimes even few hundreds) to cover given geographical area with signal. Sometime it is necessary to ensure efficient distribution of digital signal, multiple transport streams with partially different content to different groups of transmitters located in particular regions. Transport stream is a bitstream, being created according to the rules of transmission protocol, for data transmission. Within digital TV and radio networks, there are transport streams generated at different layers.
Transmitter are getting digital signal from a broadcast center in a form of transport stream, which we define as transport stream II. for sake of clarity. In majority of standards for non mobile fixed digital TV networks, whether DVB (European standard), ATSC (USA one) or ISDB (Japanese one), transport stream II. are generated in MPEG-2 TS format, following international standard ISO-13818-1.
Transmitters can be operated as SFN networks (single frequency network is network, where several transmitters is transmitting at the same frequency, or as MFN networks (multi frequency networks). In case of SFN networks, in line with ETSI TS 101 191 standard, transport streams II, are before a distribution network SFN adapted, what means so called MIP inserter, which they are passing through, inserts additional time information, which are utilized by SFN transmitters (after transport stream II. passes distribution network), in parallel of GPS signal reception for precious time synchronization of transmission by multiple transmitters. Requested time precision within SFN networks is in a range of dozen of nanoseconds.
Transport streams II, serve for transmission of transport streams I. Transport stream I. packets are typically longer than transport stream II. packets, so they are segmented to smaller parts, which are, following rules of given transport protocol mapped to transport stream II. packets. In case of digital TV transport streams I. are so called program elementary streams (PES), which serve for transmission of I, B, P video frames, generated by AV encoder, compressing AV signals.
In case of DVB-H signal transport stream I. is formed by IP packets, which in form of RTP/UDP packets bear encapsulated I, B, P AV frames generated by AV encoders.
For the purpose of differentiating transport stream, transmitting more multiplexed regionalized transport streams II, we introduce term transport stream III.
Signal transmission from broadcast center to transmitters is possible realized by different means such as satellite transmission, telecommunication terrestrial links, radio links etc.
Broadcast center is a place where transport streams II. are being generated, multiplexed and processed. Broadcast center is always placed before the distribution network. Adapters are always located at transmitters, after distribution network.
Distribution networks performs transport stream III. transmission from broadcast center to transmitters.
Transmission of multiple transport stream II. with partially different content, without bandwidth reduction, is relatively straightforward task, however distribution network transmission bandwidth is very large and equals to the sum of all particular regionalized transport streams II. bandwidth.
Because of majority of global (national) TV programs is in most of cases (typically in all) transport streams II. the same, it is technically possible, and economically advisable to reduce necessary distribution network bandwidth, without defecting and degrading of transport streams II. parameters and time synchronization.
During 2006 and 2007, 2 companies presented solution for distribution network bandwidth reduction. These solutions address signal distribution in DVB-H networks. UDCAST company, France presented solution with commercial name “iSplicer” and Thomson company, France presented solution with commercial name “EyeGate”. Common feature of those solutions is, that transport streams II. as well their SFN adaptation takes place autonomously at each transmitter, after distribution network, and not at the broadcast center, before entrance to the distribution network. Bandwidth reduction is reached by the fact, that transport streams I, in other words source data of TV programs, in case of DVB-H IP packets, are transmitted via distribution only once and do not have to be multiplied separately for each regional transport stream II. All transport streams I. are multiplexed to transport stream III. Adapter in given region from transport stream III. selects only those TV programs (PIDs), related to the given region. Transport stream II. including SFN adaptation is generated directly within the adapter at transmitter.
These solutions have several disadvantages:
They are limited only to DVB-H networks.
ETSI TS 101 191 standardizing transmission of transport streams II. in SFN networks defines single SFN adapter (MIP inserter) for all transmitters within single SFN cell. Both above mentioned solutions, based at generation of transport streams II. and SFN adaptation at transmitters are in contradiction with this standard.
These solutions involve risks of SFN network de-synchronization, transmitting interfering signals (for example in case of different packets losses at different transmitters within same SFN cell, during satellite transmission), as well as high requirements for managing and controlling of such network as well such solutions are more fragile (lost of precise synchronization, chaining errors) etc.
Disadvantage of above mentioned solutions is impossibility of monitoring transport streams II, entering transmitter's modulators, at the broadcast center.
In case when operator of transmitter network is different from operator of broadcast center, it is impossible to define clear determination point for signal and responsibility takeover.
Disadvantage is dependability of these solutions on broadcast center equipments, what among other things eliminates to use 3rd party SFN adapters.
Another disadvantage is non support of network adapter architecture.
Disadvantage is the need to eventually adapter's modification or replacement in case of standards changes.
Disadvantage is also inability to facilitate interactive communications in between of transport stream II. generators and other equipment at broadcast center like AV encoders, EPG, ESG generators, FLUTE servers and others.